Gimbal mounts are often used for precise Line of Sight (LOS) pointing in systems such as antennae, cameras, telescopes, turrets, and the like. In general, gimbals are support structures which can pivot about one or more axes. For example, a two-axis gimbal system may include two gimbals, with each gimbal configured to rotate about a different, orthogonal axis. An outer gimbal may mount to a base platform and rotate about an axis passing through this mounting point. An inner gimbal may mount to the outer gimbal and rotate about an axis perpendicular to the axis of rotation of the outer gimbal. Two-axis gimbal systems are often deployed for LOS pointing, rather than higher-order gimbal systems, due to their simplicity of operation and lower cost.
However, control problems arise when attempting to point two-axis gimbals (e.g., azimuth-elevation gimbals) at +90° elevation (“zenith”) and at −90° elevation (“nadir”). Notably, at gimbal zenith and nadir, the LOS is parallel to the azimuth axis of rotation. As a result, rotation about the azimuth axis does not move the LOS. This loss of azimuth pointing control is an example of a phenomenon referred to as “gimbal lock.”
Control of azimuthal pointing is further complicated when the gimbal is attached to a moving platform. Notably, motion of the platform causes the gimbal LOS to move its position independently of movement by the gimbal axes. Accordingly, the gimbal axes must move to counteract the base motion of the platform in order to steady the LOS.
While control systems have been developed to stabilize LOS pointing in two-axis gimbal systems at or near gimbal zenith/nadir, these systems still exhibit significant error in azimuth pointing control. Accordingly, there is an ongoing need for improved systems and methods for azimuth control in two-axis gimbal pointing systems at near-nadir/zenith elevations.